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1st Iberian Ecological Society Meeting (2019); XIV Congreso Nacional de la Asociación Española de Ecología Terrestre (AEET), Ecology: an integrative science in the Anthropocene, 4-7 February 2019, Barcelona, Spain, Marine phytoplankton produce dimethylsulfoniopropionate (DMSP), which, upon release into the ambient water, is mainly degradedby Bacteria either via the DMSP cleavage or demethylation pathway. It has been hypothesized that the extent of DMSP demethylationdepends on DMSP availability and bacterial sulfur demand, which could lead to potential niche differentiation of the demethylatingbacterial community. In this study, we determined DMSP concentrations in marine snow and the ambient water over a seasonalcycle. Subsequently, we linked these DMSP concentrations to the abundance of Bacteria harboring the dmdA gene encoding the en-zyme that catalyzes the demethylation reaction. In marine snow, DMSP concentrations were up to four times higher than in the am-bient water and three times higher in marine snow in summer than in winter. Certain subclades of demethylating Bacteria weredetected only in the ambient water and some of them exhibited strong seasonal dynamics. The demethylating bacterial communityin marine snow expressed weaker seasonal dynamics than in the ambient water. The strong correlation of the representative oligo-types of the demethylating bacterial subclades with DMSP concentrations suggest a distinct and fine-tuned niche partitioning amongdemethylating bacterial subclades. Our results reveal a pronounced seasonal variability and spatial heterogeneity in DMSP concen-trations and the associated demethylating bacterial community and point to the occurrence of specific oligotypes with differentaffinities for DMSP in coastal waters where marine snow is present